Ch 33.6: Echinoderms

Deuterostomes Part 1

body plan

endoskeleton: covered by thin epidermis, made of hard CaCO3 plates

oral and aboral surfaces

water vascular system

deuterostome shared characteristics

• radial cleavage

• enterocoelous

  • formation of the coelom from pouches that are "pinched" off of the digestive tract or archenteron during embryonic development

• mouth forms at end of embryonic stage opposite to blastospore

water vascular system

used for locomotion, feeding, or gas exchange

process:

• water enters through the madreporite

• enters stone canal and into the ring canal

• moves into the radial canals in the rays

• move into lateral canals in the radial canals

• moves into the ampules in the tube foot

  • other end of tube foot has podia (has muscles to extend) — used to suction

echinodermata

spiny skin

echinoderm mobility?

mostly sessile or slow moving

habitat?

marine; found in estuaries (where freshwater meets the ocean)

reproduction

• diecious but not sexually dimorphic (males and females are the same)

• epidemic spawning (no mating)

  • males and females simultaneously release gametes into the water

development

• deuterostomes, triploblasts, and coelomates

• 2 types of larvae: larva is bilateral, so the organism is considered bilateral (secondary radial symmetry organisms)

  • bipinnarial: 2 wings

  • pluteus

• complete digestive system

systems

• no circulatory or excretory system (undergo diffusion)

• cardiac and pyloric stomach

• respiratory: dermal branchia aka skin gills (usually)

• complete digestion

• decentralized NS: nerve ring and nerve canals

• muscle: muscles in ampulla

echinoderms and human embryological development

when the sperm and egg fertilize, a fertilization envelope forms to prevent polyspermy

classes

• Asteroidea (sea stars)

• Ophiuroidea (brittle/basket stars)

• echinoidea (sea urchins, sand dollars, sea biscuits)

• Crinoidea (sea lilies, feather stars)

• Holothuroidea (sea cucumbers)

Asteroidea

legs = rays

exhibit pentamerous radial symmetry

• rays radiating from central disk

regenerative properties

gut evagination

dermal branchia and pedicellariae (spines)

tube feet: act like suction disks through muscular and chemical processes

infraclass Concentricycloidea: sea daisies

• very small, pelagic

• incomplete digestive system

  • absorb their nutrients

• sister group to the Asteroidea

• no arms, some spines

Class Ophiuroidea

Ophus = snake/serpent

very small

distinct central disk with long, flexible (snakelike) arms

autonomize: cast off (a ray)

incomplete digestive system

some are predators/scavengers. others are suspension feeders

Ophiuroidea vs Asteroidea

Oph. do not have ambulacral groove, pedicellaria (spines), ampules, can reproduce asexually (binary fission)

Class Echinoidea

echin = spines

no arms but five rows of tube feet

Aristotle’s lantern: chewing apparatus of sea urchins

• use them to dig themselves into the rock and hide

sea otters are the urchin’s natural predator

Class Crinoidea

Krinon = lily in Greek

sea lilies live attached to the substrate by a stalk

mostly sessile — rays and mouth face up (opposite Asteroidea)

• rays extend from mouth

suspension feeders (stars are carnivorous)

ancient group

feather stars: locomotion via long, flexible arms

Class Holothuroidea

very soft

5 rows of tube feet

• can be developed as feeding tentacles

Eviscerate: disembowel to distract predators

• can regenerate whatever they throw up

lack spines, reduced endoskeleton